The invention relates to a microporous, multilayer nonwoven material for medical applications such as disposable use in an operating room, for example.
A known, substantially-waterproof, microporous, multilayer nonwoven material is a composite or laminate of a nonwoven layer of hydrophobic microfibers covered on opposite sides by one or more other nonwoven layers. The covering layers may be bonded together by a binding agent, if desired, and all the layers are bonded together into the composite or laminate.
For medical applications such as disposable use in an operating room, the layer of hydrophobic microfibers serves to trap or filter extremely fine particles and bacteria. The covering nonwoven layers serve to prevent the emergence of the microfibers and the matter which they trap or filter out. In this manner, even the escape of bacteria is prevented. It is necessary, however, that the laminate also be substantially waterproof.
For this, water-repellent nonwovens based on polypropylene, for example, or even films are known for the covering layers. All of these materials make the laminate feel unpleasant to wear as a surgical smock, face mask, or other operating-room disposable garment, for example, however, because their very low permeability to air causes the wearer to perspire.
The individual layers of the laminate also are often so poorly bonded together that the laminate has only limited utility for large-area applications such as sheets or surgical drapes. In the case of small pieces, e.g., surgical face masks, the three-layer laminate is held together by stitching or thermal welding, but stitching is too costly for large area disposables and thermal welding presents embrittlement problems.
Although a microfiber layer can be produced in different ways, e.g., by electrostatically spinning a dielectric polymer from a volatile solvent, electrostatic spinning from a fusion, or blowing a molten polymer, electrostatic spinning from a volatile solvent is preferred for augmenting the trap or filter function of the microfiber layer with electrostatic action. It has the disadvantage, however, that only very hard and brittle polymers such as polycarbonate, polysulfone, cellulose triacetate and polystryene or mixtures thereof can be produced by electrostatic spinning from a volatile solvent such as methylene chloride. The strength of such a microfiber layer is very low. It is, therefore, necessary to cover at least one side of such a layer with a tear-resistant supporting material which, as another layer, undesirably adds cost and reduces air permeability.
Moreover, however, when this and/or the other covering layers are thermally welded to such a microfiber layer, very brittle and hard spots are produced which result in an unpleasant feel for a person wearing the material. The embrittlement also creates the danger of cracking or even destroying the microfiber layer with mechanical stress in use. This undesirably reduces the trapping or filtering function of the microfiber layer and encourages penetration and escape of the microfibers through the covering layers. The embrittlement also produces poor draping qualities which make the laminate difficult to use. The welding also destroys most of the additional filtering action desirably achieved in the microfiber layer by electrostatics.